PROJECT SUMMARY – RPL CHEN Mothers of preterm infants experience elevated stress compared to that typically associated with new mother- hood. Indeed, up to 70% of mothers of preterm infants experience postpartum depression compared to 12.5% of those delivering term infants. This is important because mental stress in women is linked with poor maternal and infant health as well as (in breastfeeding women) altered circulating levels of bioactive proteins that can transfer into milk. This project will use rigorous approaches to generate new scientific knowledge with the potential to improve clinical outcomes for breastfeeding mothers of preterm infants living in north- ern Idaho, a region classified as being rural as well as ‘frontier and remote.’ Understanding modifiable factors predisposing mothers of preterm infants to extreme stress and finding ways to lower this stress and prevent its negative impacts on maternal and infant health are important public health challenges. Serum vita- min D concentration is inversely correlated with risk of postpartum depression in women delivering term in- fants, yet interventions with vitamin D supplements have yielded inconsistent results. In addition, there have been no vitamin D intervention studies in mothers of preterm infants. There is a critical need to determine ways to lower stress, response to it, and/or depression in the vulnerable population of mothers of preterm infants. Our long-term goal is to develop interventions to improve maternal and infant health – particularly in the con- text of preterm births. The primary objective of this proposal is to determine if maternal vitamin D supplementa- tion improves mental health in mothers of preterm infants living in the Idaho panhandle. Secondarily, we will assess the impact of supplementation on human milk composition. Our central hypotheses are that 1) vitamin D supplementation improves mental health in women delivering prematurely; and 2) vitamin D supplementation beneficially modifies human milk vitamin D and immunomodulatory composition. We will test our hypotheses through a prospective, double-blinded, randomized, placebo-controlled trial with 120 mothers of preterm in- fants. Mothers will be randomized to consume either a placebo control (corn oil supplement) or vitamin D sup- plements (2,000 IU/day vitamin D3). Maternal stress and depression will be assessed by measuring sali- vary/milk cortisol and oxytocin as well as administering validated stress, depression, and self-compassion questionnaires. Vitamin D status will be assessed using serum vitamin D concentration, dietary intake ques- tionnaires, and concentration of vitamin D in milk. Holistic milk composition will be assessed by proteomics and targeted protein analyses. This study is significant and innovative because it will, for the first time, document the effects of vitamin D supplementation on stress, depression, and milk composition in mothers of preterm infants. Should our hypotheses be ...